package p2000;

import java.util.Scanner;

public class Main2001计算两点间的距离 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNextDouble()) {
            double x1 = scanner.nextDouble();
            double y1 = scanner.nextDouble();
            double x2 = scanner.nextDouble();
            double y2 = scanner.nextDouble();

            double result = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
            //System.out.println(new DecimalFormat("#.00").format(result));
            System.out.println(String.format("%.2f", result));
        }
    }

}
